1. Field of the Invention
The present invention relates to an air sampling method and sensor system for spectroscopic detection and identification of chemical and biological contaminants. More specifically, the invention relates to a porous film composed of select materials to be used as an environmental sampling tool for optical and/or spectroscopic interrogation of captured solid (e.g., dust or asbestos particles), liquid (e.g., chemical warfare agents), liquid-aerosol (e.g., oil droplets), and gas phase atmospheric constituents (e.g., volatile organic compounds).
2. Brief Description of Related Art
The process of environmental monitoring for hazardous materials presents numerous technical challenges. To date, no single platform has been shown to be capable of reliably detecting and identifying all known hazardous materials that may be present in the atmosphere. The presence of most materials can be assessed through the sequential application of a variety of analytical techniques, many of which involve the use of costly instruments, expensive reagents with limited shelf lives, and more often than not, a highly trained technician to operate the sensor, and collect and prepare the sample for detailed analysis. In the present art, a variety of environmental samples may be collected into a solution phase for further preparation or onto a solid phase adsorbent for subsequent thermal desorption and analysis. The former method (solution phase collection) is useful for particulate samples whereas the latter method (solid phase adsorption followed by collection) is applicable only to gas phase substances such as volatile organic compounds. In either case, the sample is modified somewhat by these procedures, and detection is done in a batch rather than real time mode of operation.
Mass spectrometry has been applied in a role that is somewhat related to the present collection method; however, in mass spectrometry, the sample is collected on a movable tape by impaction, which only captures solid and “sticky” liquid aerosols, and the sample must be moved into the mass spectrometer ionization chamber for interrogation at fixed time intervals rather than by a continuous real-time sampling system. Impaction is a mechanical means of capturing particulates from an air stream, by impacting the particles onto a flat surface using a high velocity airflow. It is used in air monitoring applications.
The following U.S. Patents relate to environmental air sampling and/or detection and identification of contaminants:
U.S. Pat. No. 6,405,137 (June 2002) describes a thermal imaging microscopy analysis tool only. Sample preparation is not discussed and samples must be desorbed from their substrate to be analyzed chemically by some standard chemical analysis instrumentation.
U.S. Pat. No. 6,393,085 (May 2002) describes a neutron scattering system. Sample preparation is not described, but system analyzes bulk samples.
U.S. Pat. No. 6,379,623 (April 2002) describes a piezoelectric system that emits light determined by oscillation frequency of the piezo. The system requires a separate, highly specific activation layer coating the crystal, and assumes that detection would be effected by noting the specific patterns of adsorption onto the layer, as for example is done with surface acoustic wave sensors.
U.S. Pat. No. 6,327,184 (April 2002) describes a detector based on paper impregnated with dyes that change color in the presence of liquid chemical agents. The color change is photometrically monitored in an automated fashion.
U.S. Pat. No. 6,351,983 (March 2002) describes a portable gas chromatograph and mass spectrometer used to detect and identify chemicals in the gas phase.
U.S. Pat. No. 6,314,793 (November 2001) describes a device that quantitatively draws ambient air into a chamber for analysis of gas phase materials using a separate chemical detector system appropriate for the chemical to be detected.
U.S. Pat. No. 6,305,213 (October 2001) describes a gas phase detection and identification system that relies on spectrophotometry to identify chemical vapor species by virtue of their spectral fingerprints. The chemical is separated by gas chromatography prior to being delivered to this sensor.
U.S. Pat. No. 6,277,651 (August 2001) describes a wafer-based detector comprising a diode laser in the wafer and antibodies or DNA fragments that bind specific analytes to the wafer surface. The binding event is recognized by a detector that monitors the diode laser illumination.
U.S. Pat. No. 6,237,397 (May 2001) describes an acoustic wave sensor that monitors an adsorbent for a change in mass caused by absorbents. The surface must selectively adsorb materials in order to effect unambiguous identification.
U.S. Pat. No. 6,212,939 (April 2001) describes uncoated cantilevers illuminated by a scanned-wavelength photon source. The photon source excites change carriers into or out of the surface states depending on the electronic energy levels of any adsorbed materials.
U.S. Pat. No. 6,100,975 (August 2000) describes a Raman spectrometer using an external cavity laser source and a sample cell that is monitored by the spectrometer. The cell is a flow-through design and does not collect, pre-concentrate, or archive samples.
U.S. Pat. No. 6,087,183 (July 2000) describes an air sampling system consisting of a thin fluid film across which air is circulated. In the process, particulates and soluble organic substances may be analyzed by some suitable analytical method to detect and identify the contaminants. The patent suggests photometric or electro-analytical methods for such analyses.
In summary, there is a need for a sampling method and sensor system for spectroscopic detection and identification of chemical and biological contaminants that reliably detects and identifies all known hazardous materials in the atmosphere in a real time mode of operation without modification of the sample.
It is therefore an object of the present invention to provide a sampling method and sensor system that quickly identifies hazardous materials in the atmosphere in a real time mode of operation.
It is a further object of the present invention to provide a sampling method and sensor system that does not modify the sample.
It is still a further object of the invention to provide a sampling method and sensor system that can collect and identify liquid, gaseous and solid materials from the environment in a single step onto a single substrate.
It is still a further object of the invention to provide a sampling method and sensor system that is capable of demarcating the substrate so that various sampling areas on the substrate can be archived and retrieved for further analysis in a forensic laboratory or entered as forensic evidence.
These and other objects of the invention will become apparent upon further reading of this disclosure.